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An experimental breast-cancer drug stopped progression of an incurable form of the disease for
more than two years in a study, a dramatic delay for those with the second-deadliest cancer in
women.

Patients were given Pfizer’s new drug, called PD 0332991, along with Novartis’ Femara.The
findings, reported yesterday at the San Antonio Breast Cancer Symposium in Texas, showed no tumor
progression for a median of 26.1 months, compared with 7.5 months in those who received Femara
alone. The results were from the second of three stages of testing normally needed for U.S.
approval.

The medicine is the first in a new class of agents that works by blocking a protein critical in
the cancer-cell cycle, said lead researcher Richard Finn. It’s also among the most promising in
Pfizer’s drug-development pipeline, with the potential for generating $5 billion in annual sales
for breast and other tumor types, Andrew Baum, an analyst at Citigroup in London, wrote in a note
to investors.

“This magnitude of benefit is probably one of the largest with any new agent in breast cancer,
or perhaps any solid tumor,” Finn, an associate professor of medicine at the Jonsson Comprehensive
Cancer Center at the University of California-Los Angeles, said in a telephone interview. “It’s
dramatic to see this level of benefit with a new agent.”

The findings are noteworthy because of the size of the benefit and comparative safety of the
experimental treatment, said Claudine Isaacs, an oncologist and professor of medicine at Georgetown
Lombardi Comprehensive Cancer Center in Washington. The study, involving 165 patients with
metastatic disease, was small and must be confirmed in larger trials, she said.

The study included women with tumors fueled by the hormone estrogen, the most-common type of
breast cancer. All had metastatic disease, which had spread to other parts of the body and no
longer is considered curable.

Breast cancer is the most common tumor in women. Almost 230,000 women in the United States will
have it diagnosed this year, and more than 39,900 will die from it, according to the American
Cancer Society.Lung cancer is the deadliest form of the disease for women.

“It does make you stop and look,” Isaacs said. The results are “much more marked than we
typically see. It’s hard to ignore that,” she said. “It’s not something that is changing practice
today, but it’s definitely something to keep one’s eye on.”